Auxin herbicides have proven to be effective for control of unwanted plants. Phenoxy-alkanoic acid herbicides include 2,4-D (2,4-dichlorophenoxyacetic acid), 2,4-DB (4-(2,4-dichlorophenoxy)butanoic acid), dichloroprop (2-(2,4-dichlorophenoxy)propanoic acid), dicloprop-P, MCPA ((4-chloro-2-methylphenoxy)acetic acid), MCPB (4-(4-chloro-2-methylphenoxy)butanoic acid), mecoprop (2-(4-chloro-2-methylphenoxy)propanoic acid) and mecoprop-P.
Phenoxy-alkanoic acid herbicides in the acid form have poor solubility in water and are commonly formulated as an ester, such as the methyl ester or an amine salt such as the dimethylamine salt. The Phenoxy-alkanoic esters, such as the methyl ester, are more active than the salts but are more likely to volatilize with the potential to damage off-target plants. The Phenoxy-alkanoic esters and auxin amine salts are each converted in the target plants to the acid which is active in controlling plant growth. It is desirable to formulate the acids as a stable concentrate.
Some acid herbicides from the auxin class have been formulated in the form of the acid. Volgas et al. (U.S. Pat. No. 8,426,341) discloses an acid herbicide concentrate with a specific alcohol ethoxylate surfactant which forms a microemulsion on dilution with water.
Groenewegen et al. (US 2012/0283103) describes the use of certain fatty acid amide solvents to form concentrate emulsions (CEs) and emulsifiable concentrates (ECs) of auxin herbicides. The amide solvents are said to have high solvency for water insoluble compounds in preparing concentrates in the form of an emulsion (CEs) and emulsifiable concentrates (ECs).
Concentrated emulsions (CEs) contain water which necessarily reduces the potential loading of the active. We have found that emulsifiable concentrates of Phenoxy-alkanoic acids still have poor solution stability even in amide solvents and on cold storage give rise to crystal formation in the concentrate and/or crystal formation on dilution of the concentrate to form an emulsion. Poor storage stability and the consequential formation of precipitates can disrupt effective use of the herbicide through clogging of spray equipment and/or dosing of the herbicide at a lower rate than desired.
There is a need for a more highly stable emulsifiable concentrate of phenoxy-alkanoic acid herbicides.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.